CoronaVac is Safe and Induces an Immune Response, According to a Study Published in a Scientific Journal | Vaccine

The article was published on Tuesday (17) in the scientific journal “The Lancet”.

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Phase 2 of testing a vaccine verifies the security and ability to generate a response from the defense system. It is usually done with hundreds of volunteers. Phase 1, on the other hand, is carried out by dozens of people and phase 3 by thousands. It is in phase 3 where the efficacy of the vaccine will be measured.

The participants were healthy adults ages 18 to 59 and they were randomly selected to receive two doses of the experimental vaccine: low dose of 3 micrograms, high dose of 6 micrograms, or placebo. According to the research, antibody responses were induced within 28 days after the first immunization.

• Phases 1 and 2 involved 743 healthy volunteers in China, From 18 to 59 years old. In phase 1, there were 143; in phase 2, 600.
• The vaccine has two doses and appears to be safe and well tolerated.
• The most common side effect reported was injection site pain.
• The main objective of this stage of the research was assess the immune response and safety of the vaccine.
• The study did not evaluate the effectiveness in infection prevention by Covid-19.
• More studies are needed to test the vaccine in other age groups, as well as in people who have pre-existing medical conditions.

“Our findings show that CoronaVac is able to induce a rapid antibody response within four weeks after immunization, by administering two doses of the vaccine at a 14-day interval,” said Professor Fengcai Zhu, lead author of the study.

Volunteers who received the immunizer were divided into two groups, one receiving the lowest dose (3 µg) and the other the highest (6 µg). The lowest dose was considered the most appropriate and 97% of those who received it had an immune response.

The study did not look at the vaccine efficacy rate, which represents the ratio of reduction in Covid cases among the vaccinated group compared to the unvaccinated group. The research evaluated the immune response generated, since it does not necessarily guarantee the effectiveness of the vaccine.

When analyzing the immune response, the study of phases 1 and 2 focused only on the amount of antibodies. The researchers also did not evaluate the behavior of T cells (or T lymphocytes), which are part of the immune system and can identify and destroy infected cells.

According to the research, the rate of neutralizing antibodies found in the blood of the volunteers was lower (between 2.5 and up to six times) than that observed in patients who have already been infected by Covid.

Despite this finding, the researchers told The Lancet that they believe CoronaVac can provide sufficient protection against Covid-19, an assessment they made based on their experiences with other vaccines and data from preclinical studies with monkeys.

Microbiology doctor Natalia Pasternak, who was not involved in the study, says that the neutralizing antibody rate alone does not reveal the vaccine’s protective potential.

“The antibody index is lower than natural immunity, but we have to understand how they made this comparison. We still don’t know what the correlate of protection is. That is, we do not know how much antibody is needed to have protection“, explains Natália Pasternak, a researcher at the University of São Paulo.

Currently, CoronaVac is in the third and final phase of testing, when evaluated in humans. In Brazil, the group of volunteers is made up exclusively of around 10,000 health professionals, but the goal is to expand the research to 13 thousand volunteers, including children and the elderly. By October 15,000 vaccines had been applied. Each volunteer should receive two doses.

“CoronaVac can be an attractive option, as it can be stored in standard refrigeration, such as the flu vaccine. It can also be stored for up to three years, which would offer some benefits for distribution. But nevertheless, Phase 3 studies will be crucial before any recommendation, “said Gang Zeng, one of the study’s authors.

Steps to produce a vaccine

When testing a vaccine: normally divided into phases 1, 2 and 3 – scientists are trying to identify serious adverse effects and whether immunization was able to induce an immune response, that is, a response from the body’s defense system.

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Phase 1 testing often involves dozens of volunteers; those of phase 2, hundreds; and phase 3, Thousands. These phases are generally carried out separately, but due to the urgency of finding a Covid-19 vaccine, several companies have conducted more than one step at a time.

Before testing in humans, vaccines are tested on animals, usually mice and then monkeys.

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